Insulating boom and method of manufacture



NOV. 26, 1968 c, w warm- ET AL 3,412,761

INSULATING BOOM AND METHOD OF MANUFACTURE Driginal Filed Sept. 28, 19642 Sheets-Sheet 1 INV NTOR5. Cum/s N 52251.1. BY ALAN 7. mew/-5- Nov. 26,1968 c. w. VERRELL ET AL 3,412,761

' INSULATING BOOM AND METHOD OF MANUFACTURE Original Filed Sept. 28,1964 2 Sheets-Sheet 2 mvsmoas. Cum/s W VEEEELL BY ALAN 7. VALENTINEATTORNEYSv 3,412,761 INSULATING 1500M AND METHOD OF MANUFACTURE CurtisW. Verrell and Alan T. Valentine, Fairview Park, Ohio, assignors to TheUhio Brass Company, Mansfield, Ohio, a corporation of New JerseyApplication Sept. 28, 1964, Ser. No. 399,437, which is acontinuation-in-part of application Ser. No. 195,155, May 16, 1962.Divided and this application June 9, 1966, Ser. No. 569,779

6 Claims. (Cl. 138-153) ABSTRACT OF THE DISCLOSURE This inventionrelates to an article of manufacture which is a composite boom structureformed from resin bonded glass fiber mat, resin impregnated woven glassfiber roving wound transversely to the axis of the boom and containinglongitudinally disposed woven glass fiber tapes to increase the strengthof the boom.

This application is a division of co-pending application Ser. No.399,437, filed Sept. 28, 1964, which, in turn, is in part a continuationof application Ser. No. 195,155, filed May 16, 1962, now abandoned.

This invention relates to insulating booms and methods of manufacture.

The application concerns particularly booms and arms of the type whichmay be used in connection with Faraday cages and like apparatus forworking high tension power lines while energized without requiringpersonnel to utilize insultating gloves or the like.

An object of the invention is to assure the safety personnel byproviding booms which are sound and effective insulators when installed,but which also retain their insulating properties when exposed to rain,fog and inclement weather.

A further object of the invention is to provide booms which are light inweight, yet mechanically strong, which' are durable, and which may bemanufactured easily and at relatively small expense.

Other and further objects, features and advantages of the invention willbecome apparent as the description proceeds.

In carrying out the invention in accordance with a preferred formthereof, a metal mandrel of appropriate crosssectional shape accordingto the desired cross-sectional shape of the boom is coated with layersof glass fiber material impregnated with resin. Preferably, this isaccomplished by coating a mandrel of metal such as steel with a layer ofglass fiber mat impregnated with resin, curing the mat layer, dippingwoven glass roving in liquid resin, wrapping the dipped woven glassroving around the mat layer and curing the resin in the woven glassroving. Tapes of woven glass fiber roving are laid along the length ofthe mandrel between the successive turns of the woven roving of whichthe boom is formed. According to the invention, the tapes may be appliedin various positions and in various lengths to strengthen the walls ofthe boom, or the successive tapes applied along any one side of the boomcan be ofvarying widths to form a crowned surface.

A better understanding of the invention will be afforded by thefollowing detailed description considered in conjunction with theaccompanying drawing, in which:

FIG. 1 is a fragmentary view with portions broken away of a hollow boomconstructed in accordance with the invention;

FIG. 2 is a view of a cross-section of the boom of FIG. 1 represented ascut by the plane 22 of FIG. 1;

States Patent "ice FIGS. 3 and 4 are views of other cross-sections ofthe boom of FIG. 1 represented as cut by the planes 33 and 44,respectively;

FIG. 5 is a fragmentary enlarged view in section of a portion of FIG. 1to illustrate the construction in greater detail;

FIGS. 6 and 7 are views corresponding to FIG. 5 showing in greaterdetail portions of the corner of the section of FIGS. 3 and 4,respectively;

FIG. 8 is a diagram partially in section illustrating the method offorming the boom of FIG, 1 and illustrating mechanism employed therefor;and

FIG. 9 is an elevation of the glass fiber winding apparatus andimpregnating apparatus of FIG. 8.

Like reference characters are utilized throughout the drawing todesignate like parts.

For the sake of lightness and strength the boom is in hollow form.Although circular, rectangular or other cross-sections may be employed,if desired, for the sake of illustration the invention has beenillustrated in connection with a square cross-section boom. Asillustrated in FIG. 2, the upper and lower sides of the boom are madethicker and with curving outer surfaces. This not only providesreinforced corners and increased tensile and compressive strength atthese sides, but serves to drain moisture from the horizontal surfacesof the boom to prevent moisture accumulation and to insure that surfaceinsulating properties of the boom are retained in rainy weather forinsuring safety to personnel.

As indicated in FIG. 1, the boom 10 may be constructed with maximum wallthickness at one end 11, assumed to be the supported end, and minimumwall thickness at the oposite end 12, and intermediate portions such asthe portion 13 of intermediate wall thickness.

As shown in FIGS. 5, 6 and 7, the boom 10 comprises a plurality oflayers of insulating material 14, preferably a material of high degreeof insulating properties which has no tendency to absorb moisture suchas fiber glass fabric material. In order to increase the strength andform a unitary, integral whole, the glass fiber fabric is impregnatedwith a suitable plastic such as a polyesterstyrene resin. Thickening ofthe upper and lower sides 15 and 16 is accomplished by interleavingtapes 17, 18 and 19 with the layers of glass fiber fabric material onthe upper and lower sides.

Curving of the outer surface 21 of the upper and lower sides 15 and 16is accomplished by making the tapes of different width. As shown,successive groups of tapes 17, 18 and 19 are made progressivelynarrower. The groups of tapes may also be made of different lengths.

In constructing the booms illustrated, preferably a steel mandrel 22 isemployed. Where the boom is to have a square inner cross section, themandrel 22 is also of square cross section. A smooth surface steelmandrel is preferably employed. Prior to applying the glass fiber fabricmaterial, the mandrel may be waxed and polished. Then a parting orrelease agent, such as polyvinyl alcohol, may be applied to the surface.When this is done one coat is applied in liquid state with a soft clothand dried. The wax employed in this procedure may be a carnauba wax.

The use of a separate parting agent may be obviated by an alternativeprocedure in which the steel mandrel is coated with a silicone grease.Such silicone grease not only serves to cause the mandrel to be releasedreadily from the finished boom but also provides a water repellentinterior surface to the hollow boom. This makes it unnecessary to employany further step after the mechanical production of the boom has beencompleted such as coating or spraying or otherwise treating the interiorsurface of the boom to give it good electrical insulating properties sothat the boom may be used safely in conjunction with work on very hightension electrical power lines.

The first layer of glass fiber material is preferably in the form ofchopped strand mat in which the fiber strands are bonded together by apartially cured resin, so-called B-stage resin, in liquid form, whichencapsulates the strands, such as is manufactured by Ferro Corporation.This resin is a modified silane, the simplest silicone hydride (SiH witha suitable inert filler. One layer of 1 /2 ounce chopped strand mat iswrapped around the steel mandrel 22, thus covering it and the strand matis impregnate-d with an unpigmented resin, which prevents slippage whenthe woven roving is started. A suitable resin is a polyester-monomermixture, for example, maleic anhydride/pentaerythritol polyester andeither vinyl toluene or styrene, such as the polyester-monomer sold bythe Interchemical Corporation as IC-1333 or IC-1333A. The resin employedis combined with a promoting or initiating agent such as a 2% solutionof cobalt naphthenate or cobalt octoate and catalyzed with a suitablecatalyst such as a 60% solution of methyl ethyl ketone peroxide. Thislayer is then allowed to cure and harden. The foregoing liquid resin isself-setting and not thermosetting. As a result of the exothermicchemical reaction produced by the presence of the promoting agent andcatalyst, sufiicient heat is generated, to raise the temperature of thecomposition and cause curing to take place without necessity for an ovencure or a postcure.

Subsequent layers 14 of glass fiber material are in the form of wovenglass fiber roving 23, preferably of the kind having a partially curedresin coating on the fibers. In order that the woven roving may readilybe applied to the mandrel, the Woven roving is first wound upon astorage tube 24, as illustrated in FIG. 8. The woven r oving roll-23 isplaced on support bearings (not shown) adjacent a trough shaped tank 25arranged as a dip tank. Enough of the woven roving 23 is unwound toreach into the dip tank 25 and up to the mandrel 22. A steel bar 26 isplaced on top of the Woven roving to hold it in the bottom of the diptank 25.

A pigmented plastic may be employed for impregnating the woven roving.If a yellow coloring is desired, a yellow paste pigment, such as thatsold by the Ferro Corporation as V-900, is employed. Thepolyester-monomer resin, yellow pigment, cobalt naphthenate promoter orinitiator and methyl ethyl ketone peroxide catalyst are thoroughlyblended and poured into the dip tank 25 in suflicient quantity to bringthe level 27 of the liquid resin mixture over the top of the bar 26. Thesaturated woven roving is then applied to one surface of the mandrel 22,to a flat side if the mandrel is other than round in shape. Preferably,however, until the last layer is reached, unpigmented, clear plastic isemployed. This enables the winder to observe the presence of any airbubbles under a plastic-soaked layer of fabric and to press them outbefore winding on the next layer.

A fabric roller (not shown) is used to press the woven roving firmly inplace and to squeeze out any air bubbles which may have formed.Thereafter, la grooved metal roller (not shown) is used to insurecomplete saturation of woven roving and to work out any entrapment ofair between layers of woven roving and strands of glass. A suitableinstrument such as a plastic paddle or a rubber squeegee (not shown) isthen used as a squeegee to work out excess resin. If a rubber squeegeeis used, it is similar to a winder washers squeegee but composed of asuitable rubber compound which is not attached by the plastic or solventemployed in the process. Each layer is applied in this manner until thedesired thickness of wall of the boom is achieved. It will be understoodthat for rotating the mandrel 22 as successive layers of woven glassroving are applied, a suitable drive is employed including, for example,a motor 28 with a reduction gear 29 connected by means of adisengageable coupling 31 to the shaft 32 carrying the mandrel 22.

Glass fiber finish material is then applied. For example, if desired,chopped strand finish mat may then be applied dry, in a spiral patternas the mandrel revolves continuously at a slow speed. Thereafter, thefinish mat may be rolled and squeegeed in the manner already describedfor the woven glass roving and followed by another layer of finish matin a spiral pattern with the spinals intersecting the spirals of thelayer below at approximately followed by rolling and squeegeeing. Theentire boom or arm and the mandrel are then allowed to revolve until thearm has cured and hardened.

Alternatively, instead of the spiral layers, the two final layers ofwrap may consist of two layers of fiber glass cloth of a widthcorresponding to the length of the wound portion of the mandrel,suitably rolled and squeegee-d as previously described. A fiber glasscloth such as that sold by the Exeter Manufacturing Company may beemployed.

Assuming that a clear unpigmented plastic has been employed inimpregnating the previous layers, the final layer or the final twolayers of glass cloth are pigmented by pouring on the pigmented resin.

When the boom has cured, the mandrel is removed from the drive unit29-31 and placed in a withdnawal fixture (not shown). The mandrel 22 isthen pulled out of the glass fiber boom. In the case of relatively smallarms the glass fiber plastic arm may then be placed in a gas fired ovento postcure at approximately F. for about two hours. However, it hasbeen found that this is not necessary since by employment of suitablechemical composition in the plastic the exothermic chemical reactionproduces enough elevation of temperature above room temperature forcuring. Infrared radiation may also be employed, if desired, for curinganms which are too lange to place in an oven for postcuring.

Following the open room chemical curing, or the furnace postcuring, ifemployed, the boom may then be finished by sanding smooth. Sanding,however, is unnecessary in order to obtain a smooth surface. A smoothsurface may be obtained without sanding as a result of curing of theouter surface of the resin impregnated layer. The smooth surface is thencoated with pigmented, promoted and catalyzed resin applied by brush.The boom is then ready to be fitted with such metal parts as may berequired (not shown) and to be installed in the equipmerit in which itis to be used.

In order to provide additional strength to the tension and compressionsides of the boom, the top and bottom sides 15 and 16, respectively,additional single layers of woven roving tapes such as the tapes 17, 18and 19 are placed on the compression and tension sides, one at a timeafter each layer of woven roving has been completed. In the course ofbuilding up the boom the tapes also will become impregnated with resin.This impregnation may be accomplished by saturating the tapes With resinfrom the dip tank 25 and rolling and squeegeeing between layers of thecontinuous, wrapped-around woven roving material 23. Alternatively thetapes need not be themselves dipped in the dip tank but merely laid onthe top side of the mandrel on the previously wound layer of fabric,which permits the tape to soak up resin from the layer of rovingmaterial below as well as the next layer of roving material when thatlayer is wound on. When the tape itself is not dipped into the dip tank,the roller used for rolling and squeegeeing before Winding on the nextlayer of roving material is dipped into the dip tank.

Various arrangements of tapes may be utilized to produce desiredstructural characteristics in the boom. Thus, all of the tapes 17, 18and I? may be of the same width and extend the entire length of the boomin order to strengthen the top and bottom walls of the boom. Again, thetapes may be arranged in groups having the lengths of the sections 11,11 and 13, and 11, 13 and 12, as illustrated schematically in FIGS. 2, 3and 4. In this way, the lightest weight can be achieved for a desiredstrength of the boom inasmuch as the boom is supported along the section11 and the load is applied to the outer extremity of the section 12. Therectangular hollow construction, especially when reinforced with theadditional layers of tape, is structurally stronger from both ageometric and mechanical standpoint than circular cross-section boomsbecause there is more material in a rectangular cross section than in around tube of the same size. This makes the structural members so formedstronger especially in tension and flexure, which are both important instructural members such as booms.

FIG. 5 illustrates an arrangement of the tapes particularly useful inbooms intended for use in energized line working. As there shown, thetapes vary in width with the widest tape close to the steel mandrel andhaving a transverse dimension only slightly less than the full width ofthe boom, and the narrowest tape close to the outer surface of the boom.This arrangement provides a convex contour or crown on the outer surfaceof the boom and serves to promote drainage of water and other foreignsubstances off the sides of the arm. This prevents water from drainingdown the full length of the arm and providing a path for current whichcould result in a short circuit or ground endangering the life of a manin the bucket of a Faraday cage or endangering other personnel on theground.

In the alternative procedure, described at pages 4 and 5, in whichsilicone grease is applied to the steel mandrel to perform the functionof a parting agent, it has been found that the silicone material isembodied in the hardened resin of the first layer of glass fibermaterial on the interior of the boom. Thus, the silicone material isdispersed through the polyester resin body of the first layer of glassfiber material along the interior of the boom, as well as beingdispersed over the interior surface of the boom. The silicone grease,above referred to, is one form of silicone material useful for thispurpose and may comprise a commercially available silicone grease, suchas that sold by the General Electric Company under the designation ofX4005 or X84006. The presence of the silicone material minimizestracking effects which would otherwise result from the application ofhigh voltages, and particularly prevents the formation of conductivefilms of water due to the deposition of water vapor, fog, etc., on theinterior of the boom.

For further assuring the maintenance of an insulating surface, a layerof silicone grease, such as that sold by the General Electric Companyunder the designation X84006 or X4005, is applied to the outer surfaceof the boom. As previously explained, the inner surface of the hollowboom is already coated with silicone grease as a result of the greasingof the mandrel with silicone grease before the winding is commenced.However, satisfactory results have also been obtained where siliconegrease had not been applied to the mandrel by applying a liquid solutionto the inner surface to maintain its insulating properties. For example,a liquid which can be used is a silicone oil solution composed of onepart No. F145 silicone oil and one part xylene, as sold by the DowCorning Company. The silicone coating provides further insulation andavoids contamination of the boom which could cause a short circuit orground.

If desired, the curving outer surface of the top and bottom sides of theboom may be achieved by the utilization of a mandrel of special shapewith the desired surface curvature in the top and bottom surfaces of themetal mandrel. In this manner a curved cross-section of the top andbottom surfaces of the boom would be provided both inside and outside.It would be unnecessary to provide splices or interleaved tapes ofdifferent widths in order to achieve the curvature of the surface andonly tapes of the maximum width would be required. The full width tapeswould give a stronger laminate and avoid the necessity for stockingseveral different widths of woven roving.

Certain embodiments of the invention and certain methods of operationembraced therein have been shown and particularly described for thepurpose of explaining the principle of operation of the invention andshowing its application, but it will be obvious to those skilled in theart that many modifications and variations are possible, and it isintended therefore, to cover all such modifications and variations asfall within the scope of the invention.

What is claimed is:

1. A non-conducting boom constituted as a hollow tubular structuralmember, comprising an inner layer of glass fiber mat, a continuouslength of woven roving of glass fiber extending transversely about thelongitudinal axis of the member in a plurality of successivelyoverlapping layers, and tapes of woven roving disposed longitudinallybetween successive layers of the said layers of woven roving, and curedresin extending throughout the mat, roving, and tapes, and the saidtapes comprising a structural reinforcing means for the said boom.

2. A boom in accordance with claim 1, with tapes of progressivelydecreasing width between successively outward layers to form a generallycurved outer surface.

3. A boom in accordance with claim 1, with the tapes in different layershaving progressively decreasing length between successively outwardlayers.

4. A boom in accordance with claim 1, with an adherent coating of resinon the fibers of the glass mat and silicone material dispersed in theinner layer along the interior of the member and coating the interiorsurface thereof.

5. An insulating member in accordance with claim 4, in which thesilicone material in the resin of the body is formed from a layer ofsilicone material applied as a parting agent on the surface of a mandrelon which the member is formed during manufacture thereof.

6. An article of manufacture as in claim 1 wherein the glass fiber matis composed of chopped strand.

References Cited UNITED STATES PATENTS 1,400,078 12/1921 Kempton 1381412,525,272 10/1950 Rhoton.

2,594,838 4/1952 Alexander et al. 138156 X 2,742,931 4/ 1956 Ganall138144 2,929,409 3/1960 Waehner 138141 2,674,297 4/ 1954 Greenwald 1382,943,009 6/1960 Mirsky et a1 138 3,212,664 10/1965 Wagle 156191 XRLAVERNE D. GEIGE-R, Primary Examiner. B. KILE, Assistant Examiner.

